Abstract: A process is disclosed for preparing a carbon molecular sieve used for the separation of oxygen from nitrogen, which comprises the steps of:(a) milling hard coal to a grain size of 95%<20.mu.m;(b) oxidizing the finely milled hard coal with air in a fluidized bed;(c) adding water and coal tar pitch as a binder and molding the finely milled hard coal into shape;(d) carbonizing the finely milled hard coal molded into shape in a rotary kiln at a temperature of 500 .degree.to 850.degree. C., with a dwelling time of 55 to 65 minutes, in order to obtain a carbonization product with a bulk density of 530 to 560 g/l;(e) activating the carbonization product with steam at to 900.degree. C. for 165 to 195 minutes to obtain a sintered carbonaceous product having a bulk density of 590 to 650 g/l; and(f) treating the sintered carbonaceous product at 750 to 850.degree. C. with carbon-splitting hydrocarbons to obtain said carbon molecular sieve.